Decomposition of CGA leads to
the production of two very important
components. As seen in Figure 2, the
decomposition of CGA causes a steady
increase in caffeic and quinic acid, both of
which are classified as phenolic compounds.
Such compounds are often astringent in
nature, thus darker roasts tend to produce
coffees higher in astringency and body. The
same principle is seen when we compare the
body and astringency of a red wine, such as
a cabernet, to that of a chardonnay. As a rule
of thumb, any naturally occurring substance
that exhibits color will always contain a
large concentration of chromophores, a
class of colored phenolic compounds.
Recently, CGA has also been suggested
as the main culprit for people suffering
from acid reflux. It’s been estimated
that as little as 200 mg. of CGA can
increase levels of HCl in the stomach.
A typical cup of coffee yields anywhere
between 15 and 325 mg. of CGA, well
within the suggested range. Those
drinking decaffeinated do benefit,
as the decaffeination process results
in a slight decrease of CGA content.
But it should be noted that the initial
increase in stomach acidity is due
solely to CGA and not caffeine as
many are lead to believe.
CGAs: Quinic and Caffeic
Before the first crack, CGA
continues to decompose, while
quinic acid progressively increases
in concentration. Being a phenolic
compound, quinic acid also
proportionally increases body and
astringency and forms colored
compounds, namely melanoidins.
Interestingly, increases in quinic
acid concentration have been
documented in cases where green
coffee is stored for an extended period
of time in warehouses, at times up
to 1.5 percent dry basis. Luckily, one
does not need to wait months to see
the immediate affects on acidity, as it
can be demonstrated in any cupping
lab. As most of us have experienced
while cupping, the longer we leave
out a coffee liqueur while cooling,
the greater its perceived acidity. Why
this happens is only one part of the
fascinating chemistry that occurs in
our morning cup of joe.
At roast levels exceeding 6.5
percent dry basis—roughly cinnamon
roast—we begin to see the formation
of quinide, the same compound
commonly found in tonic water. As
this compound remains in the hot
infusion, it slowly hydrolyzes back to
quinic acid and serves to increase the
level of perceived sourness. Thus, with
dozens of reactions invisibly taking
place in the cup, it truly makes cupping
an extremely difficult time-dependent
exercise. Away from the cupping lab,
the effect is also seen when coffee has
been left sitting on a heating element
for an extended period of time. This
is all too common during long road trips, when we’re welcomed
at the nearest highway coffee shop with sour coffee, and when we
hear stories of unscrupulous coffee shop managers leaving their
coffee on the heating pan for up to eight hours on end, only to serve
it “fresh” to you. Unfortunately, there is no magic potion to prevent
this reaction, and we’re once again reminded of the importance of
coffee freshness.
Another one of CGA’s byproduct is caffeic acid. It is also a
phenolic compound and one that will contribute slightly to cup
astringency. Recently, caffeic acid has been documented to be a 38